Evolution and the Geologic Time Scale

The concept of geologic time and the appearance and evolution of life on Earth is VERY important to my class. One of my most favorite sayings, "Nothing in Biology makes sense except in the light of evolution" (Theodosius Dobzhansky, American Biology Teacher, 1973.) is a mantra in my classes. We can't teach cellular respiration without the concept of endosymbiosis, and we can't teach endosymbiosis until our students know the differences between prokaryotic and eukaryotic cells, etc, etc, etc. The history of life on Earth is (or should be!) woven into every single lesson we teach in a Biology class.

Then "What's the problem?" you might be asking yourself. My problem is time. Not geologic time;  just time to teach. It is a struggle to cover everything in a year that needs to be covered! My solution was to find a way to quickly cover the concepts of geologic time and the evolution of life on Earth, without taking weeks to do so.

Here are my goals.  I want my students to:

• Know what is meant by the term "geologic time scale."
• Be able to visualize the enormity of geologic time.
• Know when life first appeared on Earth.
• Know the order in which various life forms appeared.
• Know the importance of fossils, especially traditional fossils, to the study of evolution.
• Understand how scientists are able to date fossils that are found in various rock strata.
• Understand the relationship between mass extinctions and adaptive radiations.
• Have a clear and concise understanding of what happens in each era of Earth's history.

I am extremely pleased with the Geologic Time Scale activity I put together to accomplish these goals. This resource can be used in conjunction with your other lessons and materials you use on this topic, OR, (and here is the best part!) it can be used as a stand-alone activity that quickly covers the above topics in just a couple of class periods.  The printable version is perfect for traditional classroom settings, but there is also a digital Google Apps version for distance learning and 1:1 schools.

If you need to teach this fast, this is the activity for you!

What concepts are covered in this resource?

• Definition of the geologic time scale.
• How the geologic time scale was developed by scientists.
• Relative dating and Radioactive dating.
• Earth’s history is divided into 4 Eras which are subdivided into smaller periods.
• How to read the information on the geologic time scale reference table.
• Comparing lengths of geologic time.
• The order of events in the evolution of life on Earth.
• Transitional fossils.
• Estimating the age of organisms based on relative dating.
• Rock strata.

What will the students be doing?

• Students complete a 6-page handout on the geologic time scale and complete a 2-page timeline of the history of life on Earth.
• Students make a circle graph of the time spent in each era.
• Students use the included Geologic Time Scale Reference Table to answer a series of 30 problem solving questions.
• Students make a scale diagram showing the length of each era.
• Students look at pictures to evaluate characteristics of certain organisms.
• Students complete a relative dating cut and paste activity.
• Students using relative dating to estimate the age of certain organisms.
• Students complete a 2-page cut and paste timeline activity showing the evolution of life on Earth.
• Students are guided through an exercise that allows them to compare all of Earth’s history to one calendar year.

As much as I love teaching these topics, there is a limit to what we can expect our students to absorb. We can't ask them to learn every event in every era, period, and epoch in geologic time. I have certain key events that I want my students to know, so I put together a one-page table outlining the most important events in Earth's history.
  

The beauty of this resource is that with this one-page reference table the activity can be used as a stand-alone lesson. The students don't need prior knowledge or prior teaching. This lesson can be completed in two 1-hour class periods right before you begin your units on evolution. I would suggest having a biology textbook handy if students are seeing this information for the first time. There may be a few vocabulary words that they would need to look up.

If you are in a big time crunch, let the students work in groups for one class period, and complete complete unfinished portions for homework.

You can find this activity in my TpT store by clicking this link, and here is what you can expect to find included:

• 6-Page printable and editable student worksheet set
• 1-Page Geologic Time Scale Reference Table
• 2-Page Timeline Worksheet
• 8-Page Teacher Guide and Answer Keys
• All images needed for the "cut and paste" portions of the activity.
• Paperless digital google apps version for use in Google Drive, Google Classroom, Microsoft OneDrive, or similar.

I hope this article has given you something to think about, and some new ideas on how to teach geologic time to your biology or life science students. Have fun teaching!

Lab: Making Coacervates

Two activities in one:  

A guided lab activity plus a student designed lab activity!

I just tried this lab for the first time this year. And I liked it so much that I will definitely use it again next year!

Each school year I make myself try new and different activities.  The idea of this lab has been around for a long time, and when I  finished teaching my unit on "The Origin of Life on Earth" I though I would give this lab a try. The lab is called "Making Coacervates."

What are coacervates? Coacervates are simply droplets that are composed of molecules of different types.  Coacervates are not alive, but they do share some of the same characteristics as those found in living cells.  Because of this, many scientists have hypothesized that structures similar to coacervates may have been the precursors to the first living cells.  Although the origin of life has not been duplicated in the laboratory, it is very simple to observe the formation of coacervates.  This activity was a thought-provoking one for my students.  They clearly were able to see, using a microscope, how it is possible for molecules to come together to form cell-like structures.

This lab kills two birds with one stone!  The first part of my lab was a guided lab activity.  The students followed a lab procedure that I gave them to test the effect of different pH levels on the formation of coacervates.  But the second day of the lab packed a much bigger punch!!  I assigned each lab group a different variable to test.  The group had to form a hypothesis and then design a lab to test their hypothesis.  For example, some groups had to test the effect of temperature on coacervate formation, while other groups tested the effect of changing solution concentrations on the formation of coacervates.  

Six different variables were tested by the students.  At the conclusion of their experiment, each student group had to make a very short report to the class discussing the results they obtained.  This is a time consuming activity, but it is time well spent!  Common Core standards are demanding that science students spend more time in analysis, problem solving activities.  

I am particularly proud of my 5-page handout that I designed for my students to use as they designed their experiment.  I required them to form a hypothesis, write a procedure that would gather quantitative data, design a control for the experiment, describe their experimental and control groups, graph their data, form a conclusion, and much more.

Materials needed:     Glass test tube with cap, Graduated cylinders, Gelatin solution (protein), Gum Arabic (carbohydrate),  Glass stirring rod, pH paper,  .1M HCl solution, Dropping pipets, Microscope, Test tube rack,  and Microscope slides. Additional materials are needed for the student designed experiments.


What are the pros and cons of this lab?

Pros include:

• Students gained a better understanding of coacervates and how they might have formed in the seas on early Earth.
• Materials list is simple and inexpensive.
• Teaching students how to design and carry out a controlled experiment is a MUST in the science classrooms of today.

Cons include:

• This lab takes a bit of time.  Students completed the guided activity in one class period, they wrote and designed their experiment in a second class period, and they carried out their experiment in a third lab period.  Some parts of the lab report had to be completed as a homework assignment.
• The coacervates are very easy to find under the microscope, but they are difficult to count.  The student has to scan the entire slide and count the number of coacervates that were formed.  This is a source of error.

This lab was used as a conclusion to my unit on "The Origin of Life." Some of the materials I used to teach this unit can be found here:

Origin of Life PowerPoint and Notes for Teacher and Student

Origin of Life Review PowerPoint

Origin of Life Quizzes